The present invention relates to a pressure-resistant helical corrugated pipe adapted to be buried in the ground, so that telecommunication cables such as an electric cable and a telephone cable can be installed in such corrugated pipe for the purpose of protecting such cables. Also, such a corrugated pipe is used as a water main pipe, a sewer pipe, or a liquid transport pipe used in a plant or a factory.
Among such conventional pressure-resistant helical corrugated pipes, the pipes adapted for underground use have been required to be pressure-resistant in order to withstand a great ground pressure. An underground pressure-resistant pipe as shown in FIGS. 16 and 17 is conventionally known (see, for example, Japanese Laid-Open Utility Model Application No. 141889/86 filed by the Applicant of the present application). In this conventional pressure-resistant pipe, a continuous reinforcing belt plate 06 made of a thin metal plate is embedded in a pipe wall 01 and extends over a top portion 02 of the helical corrugation, opposite side wall portions 03 and 04 extending from the top portion 02, and part of a bottom portion 05.
However, since the metal reinforcing belt plate 06 to be thus embedded in the pipe wall 01 is of such a unitary construction that this plate is disposed in the top portion 02 and the opposite side wall portions 03and 04, with its oppositely-projecting side edge portions disposed in part of the bottom portion 05 as described above, the thin metal plate, when helically wound, is liable to be subjected to deformation due to strain because of variations in diameter of the thus helically-wound thin metal plate. This results in a problem that it is difficult to produce a helical pipe having a good appearance, and for this reason it has been necessary for the thin metal plate to be subjected to a special processing or working.